Regulation of IGF-2 gene expression in human chondrosarcoma derived cell lines : HCS-2/8 and -2/A

在无血管的软骨细胞中，胰岛素样生长因子-2（IGF-2）的自分泌功能对软骨细胞的生长和分化具有重要作用。人软骨肉瘤细胞系IGF-2基因表达的调控（HCS-2/8和HCS-2/A）中，IGF-2的4个启动子均在人软骨细胞中表达，并有与转录因子结合的保守序列; EGR 1（early growth response gene product 1）、SP-1（specificity protein-1）和WT 1（Wilms tumor suppressor）定位于IGF-2启动子的转录调控区域。SP-1在正常软骨细胞和HCS-2/8中的表达都很弱，但HCS-2/8中EGFR 1的表达高于正常软骨细胞，WT 1的表达低于正常软骨细胞。这表明，在软骨肉瘤HCS-2/8细胞的生长初期，EGFR 1的正性作用和WT 1的负性作用协同作用可能导致细胞的异常生长，抗坏血酸对IGF-2、H19基因表达的影响是正性的（肿瘤抑制因子）、EGFR 1、SP-1、WT 1、10型胶原α 1、聚集蛋白聚糖和碱性磷酸酶，但对2型胶原α 1阴性。这些结果表明，抗坏血酸在软骨细胞中的作用可能是从生长到分化的生长和再分化因子，IGF-2在HCS-2/8中的印迹状态是所有启动子的父系等位基因，并且似乎直接与过量基因表达无关。在<KIP2>人染色体11p15.5区域印迹簇中的CDKNIC（p57^）上，检测到HCS-2/8中父亲等位基因的PAPA重复序列中缺少PA，并且表达的等位基因是母亲的。

In chondrocytes without vascula, autocrine function of insulin-like growth factor-2 (IGF-2) is very important for the growth and differentiation. Regulation on the expression of IGF-2 gene (IGF-2) in human chondrosarcoma derived cell lines (HCS-2/8 and -2/A) was investigated in order to explore the function of IGF-2.In human chondrocytes, all four promoters of IGF-2 are expressed, and consensus binding sequenses to the transcriptional factors ; EGR1 (early growth response gene product 1), SP-1 (specificity protein-1) and WT1 (Wilms tumor suppresor), are localizing over the transcriptional regulation region of IGF-2 promoters. Although the expression of SP-1 is very slight in both of normal chondrocytes and HCS-2/8, EGR1 expression in HCS-2/8 was higher than that in normal chondrocytes and WT1 expression in HCS-2/8 was lower thatn that in normal chondrocytes. This suggests that the abnormal growth of chondrosarcoma-derived HCS-2/8 may be induced with the synergistic effect between a positive function of EGR1 and negative one of WT1 to the growth enhancement during the initial growth phase.The effects of ascorbic acid in HCS-2/8 were positive to the gene expression of IGF-2, H19 (tumore suppresor), EGR1, SP-1, WT1, type-10 collagen alpha1, aggrecan and alkaline phosphatase, but negative to that of type-2 collagen alpha1. These results suggest that the role of ascorbic acid in chondrocytes may be as a growth and differetiational factor during the phases to differentiation from growth.The imprinting status of IGF-2 in HCS-2/8 was paternal alleles for all the promoters, and seem to be independent directly on the excess gene expression. On CDKNIC (p57^<KIP2>) in the imprinting cluster over human chromosome 11p15.5 region, a lacking of PA in the PAPA-repeat was detected for the paternal allele in HCS-2/8, and the expressed allele was maternal.